Minimal string-scale unification of gauge couplings

We look for the minimal particle content which is necessary to add to the standard model in order to have a complete unification of gauge couplings and gravity at the weakly coupled heterotic string scale. Using the current precision electroweak data, we find that the presence of a vector-like fermion at an intermediate scale and a non-standard hypercharge normalization are in general sufficient to achieve this goal at two-loop level. If one requires the extra matter scale to be below the TeV scale, then it is found that the addition of three vector-like fermion doublets with a mass around 700 GeV yields a perfect string-scale unification, provided that the affine levels are kY=13/3, k2=1 and k3=2, as in the SU(5) X SU(5) string-GUT. Furthermore, if supersymmetry is broken at the unification scale, the Higgs mass is predicted in the range 125 GeV - 170 GeV, depending on the precise values of the top quark mass and tan(beta) parameter.Comment: 12 pages, 2 figures, references updated and comments added, final version to appear in Phys. Lett.

Natural Gauge and Gravitational Coupling Unification and the Superpartner Masses

The possibility to achieve unification at the string scale in the context of the simplest supersymmetric grand unified theory is investigated. We find conservative upper bounds on the superpartner masses consistent with the unification of gauge and gravitational couplings, M_{\tilde G} < 5 TeV and M_{\tilde f} < 3 \times 10^7 GeV, for the superparticles with spin one-half and zero, respectively. These bounds hint towards the possibility that this supersymmetric scenario could be tested at future colliders, and in particular, at the forthcoming LHC.Comment: 8 pages, 4 figures, version accepted in Physics Letters

Texture Zeros and Weak Basis Transformations

We investigate the physical meaning of some of the "texture zeros" which appear in most of the Ansatze on quark masses and mixings. It is shown that starting from arbitrary quark mass matrices and making a suitable weak basis transformation one can obtain some of these sets of zeros which therefore have no physical content. We then analyse the physical implications of a four-texture zero Ansatz which is in agreement with all present experimental data.Comment: 11 pages, typeset using revte

Anomaly-free U(1) gauge symmetries in neutrino seesaw flavor models

Adding right-handed neutrino singlets and/or fermion triplets to the particle content of the Standard Model allows for the implementation of the seesaw mechanism to give mass to neutrinos and, simultaneously, for the construction of anomaly-free gauge group extensions of the theory. We consider Abelian extensions based on an extra U(1)_X gauge symmetry, where X is an arbitrary linear combination of the baryon number B and the individual lepton numbers L_{e,mu,tau}. By requiring cancellation of gauge anomalies, we perform a detailed analysis in order to identify the charge assignments under the new gauge symmetry that lead to neutrino phenomenology compatible with current experiments. In particular, we study how the new symmetry can constrain the flavor structure of the Majorana neutrino mass matrix, leading to two-zero textures with a minimal extra fermion and scalar content. The possibility of distinguishing different gauge symmetries and seesaw realizations at colliders is also briefly discussed.Comment: 12 pages, 2 figures, 7 tables; comments and references added, a new subsection with nonstandard interactions of neutrinos included; final version to appear in Phys. Rev.

Mirroring its British masters: state and outsourced terrorism against the Maoist insurgency

The Indian state has been adopting controversial policies for countering the Maoist insurgency. Even worse, this behaviour seems to mirror Britishcolonial attitudes against India’s population at some level. Consequently, this article attempts to understand this probable ‘paradoxical’ conduct. Withthe support of the post-structuralist theory, I discuss state and outsourced terrorist practices of the Indian state apparatus against this insurgency. Toreach this goal, first, I try to explicate the concept of state terrorism and its application in India. Then, I analyse the historical development of theMaoist movement and India’s concrete policies of state and outsourced terrorism against this counter-hegemonic movement. I believe the British Raj’scolonial practices have had a deep dialectical influence on India’s state apparatus and major political parties to date. So, this inquiry may clarify thepersistence of colonial practices within India.The Indian state has been adopting controversial policies for countering the Maoist insurgency. Even worse, this behaviour seems to mirror Britishcolonial attitudes against India’s population at some level. Consequently, this article attempts to understand this probable ‘paradoxical’ conduct. Withthe support of the post-structuralist theory, I discuss state and outsourced terrorist practices of the Indian state apparatus against this insurgency. Toreach this goal, first, I try to explicate the concept of state terrorism and its application in India. Then, I analyse the historical development of theMaoist movement and India’s concrete policies of state and outsourced terrorism against this counter-hegemonic movement. I believe the British Raj’scolonial practices have had a deep dialectical influence on India’s state apparatus and major political parties to date. So, this inquiry may clarify thepersistence of colonial practices within India